# std::ranges::minmax_element, std::ranges::minmax_element_result

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
Call signature |  |
template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less > constexpr minmax_element_result<I> minmax_element( I first, S last, Comp comp = {}, Proj proj = {} ); | (1) | (since C++20)
template< ranges::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less > constexpr minmax_element_result<ranges::borrowed_iterator_t<R>> minmax_element( R&& r, Comp comp = {}, Proj proj = {} ); | (2) | (since C++20)
Helper types |  |
template< class I > using minmax_element_result = ranges::min_max_result<I>; | (3) | (since C++20)

1) Finds the smallest and largest elements in the range `[`first`,` last`)`.
2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

### Parameters

first, last | - | iterator-sentinel pair denoting the range to examine
r | - | the range to examine
comp | - | comparison to apply to the projected elements
proj | - | projection to apply to the elements.

### Return value

An object consisting of an iterator to the smallest element as the first element and an iterator to the greatest element as the second. Returns {first, first} if the range is empty. If several elements are equivalent to the smallest element, the iterator to the first such element is returned. If several elements are equivalent to the largest element, the iterator to the last such element is returned.

### Complexity

At most std::max(std::floor(1.5 * (N − 1)), 0.0) applications of the comparison and twice as many applications of the projection, where N = ranges::distance(first, last).

### Possible implementation

    struct minmax_element_fn
    {
        template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
                 std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less>
        constexpr ranges::minmax_element_result<I>
            operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
        {
            auto min = first, max = first;

            if (first == last || ++first == last)
                return {min, max};

            if (std::invoke(comp, std::invoke(proj, *first),
                                  std::invoke(proj, *min)))
                min = first;
            else
                max = first;

            while (++first != last)
            {
                auto i = first;
                if (++first == last)
                {
                    if (std::invoke(comp, std::invoke(proj, *i),
                                          std::invoke(proj, *min)))
                        min = i;
                    else if (!(std::invoke(comp, std::invoke(proj, *i),
                                                 std::invoke(proj, *max))))
                        max = i;
                    break;
                }
                else
                {
                    if (std::invoke(comp, std::invoke(proj, *first),
                                          std::invoke(proj, *i)))
                    {
                      if (std::invoke(comp, std::invoke(proj, *first),
                                            std::invoke(proj, *min)))
                          min = first;
                      if (!(std::invoke(comp, std::invoke(proj, *i),
                                              std::invoke(proj, *max))))
                          max = i;
                    }
                    else
                    {
                        if (std::invoke(comp, std::invoke(proj, *i),
                                              std::invoke(proj, *min)))
                            min = i;
                        if (!(std::invoke(comp, std::invoke(proj, *first),
                                                std::invoke(proj, *max))))
                            max = first;
                    }
                }
            }
            return {min, max};
        }

        template<ranges::forward_range R, class Proj = std::identity,
                 std::indirect_strict_weak_order<
                     std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
        constexpr ranges::minmax_element_result<ranges::borrowed_iterator_t<R>>
            operator()(R&& r, Comp comp = {}, Proj proj = {}) const
        {
            return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj));
        }
    };

    inline constexpr minmax_element_fn minmax_element;

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <iterator>
    namespace ranges = std::ranges;

    int main()
    {
        const auto v = {3, 9, 1, 4, 1, 2, 5, 9};
        const auto [min, max] = ranges::minmax_element(v);
        std::cout
            << "min = " << *min << ", at [" << ranges::distance(v.begin(), min) << "]\n"
            << "max = " << *max << ", at [" << ranges::distance(v.begin(), max) << "]\n";
    }

Output:

    min = 1, at [2]
    max = 9, at [7]

### See also

ranges::min_element (C++20) | returns the smallest element in a range (algorithm function object)
ranges::max_element (C++20) | returns the largest element in a range (algorithm function object)
ranges::minmax (C++20) | returns the smaller and larger of two elements (algorithm function object)
minmax_element (C++11) | returns the smallest and the largest elements in a range (function template)

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